A report in the prestigious medical journal The Lancet explains the ways in which medications are rated for their effectiveness. There are two ways this data is shared among the scientific community – the RRR rating and the ARR rating. Both ratings are required for an accurate picture.
The report – Covid-19 vaccine efficacy and effectivenes – the elephant (not) in the room makes it clear that only using the Relative Risk Reduction (RRR) rating can paint a very positive picture of a vaccine’s effectiveness. However, the more reliable Absolute Risk Reduction (ARR) system paints a truer picture (not one marketing and PR firms would look to use).
To illustrate the point, The Lancet report says: “Although attention has focused on vaccine efficacy and comparing the reduction of the number of symptomatic cases, fully understanding the efficacy and effectiveness of vaccines is less straightforward than it might seem.
“Depending on how the effect size is expressed, a quite different picture might emerge.
“Vaccine efficacy is generally reported as a relative risk reduction (RRR). It uses the relative risk (RR) – ie, the ratio of attack rates with and without a vaccine – which is expressed as 1–RR.
“Ranking by reported efficacy gives an RR – relative risk reductions of:
- 95% for Pfizer–BioNTech
- 94% for Moderna–NIH
- 91% for Gamaleya
- 67% for J&J
- 67% for AstraZeneca–Oxford
“However, RRR should be seen against the background risk of being infected and becoming ill with covid-19, which varies between populations and over time.
“Although the RRR considers only participants who could benefit from the vaccine, the absolute risk reduction (ARR), which is the difference between attack rates with and without a vaccine, considers the whole population.”
ARRs tend to be ignored, states The Lancet report, because they give a much less impressive effect size than RRRs – which are:
- 1·3% for AstraZeneca–Oxford
- 1·2% for Moderna–NIH
- 1·2% for J&J
- 0·93% for Gamaleya
- 0·84% for Pfizer–BioNTech
Safe and effective?